Arc welding apparatus



Sept. 20, 1949. FROMM 2,482,473

ARC WELDING APPARATUS Filed Nov. 3, 1948 Fig.|.

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Patented Sept. 20, 1949 UNITEDTfS'TATE s BATENffOFF I CE g ARC WELDINGAPPARATUS Kenneth N.1Fromm, Pittsburgh, Pa., assignorcto WestinghouseElectric Corporation, EastPitts- ,burgh, la., a corporation ofIfennsylvania, H Application November 3, 1948, Seriallo.' 58,137 vconfin (01. 315-24 g My invention relates, generally, arc weldingapparatus, and it has .referencein particulartoarc initiating andstabilizing systems for use .with arc welding systems or circuits.

- Generally stated, it is an objectlof myinvention to provide an arcinitiating and stabilizing system for use with arc welding circuits thatis simple and inexpensive to .manufacture and reliable and effective inoperation.- l

vide, in an arc initiating and stabilizing system,

for synchronizing-a blocking oscillator. in accordance .with the voltagein an alternating current arc welding circuit for applying dampedimpulses to the welding circuit.-

- It is animportant object of .my invention to provide, in an. arcweldingjsystem, foriusing a pulsed oscillator for initiating'andstabilizing the arc. 1 x J Another important object of myinventionis to provide, in an alternating currentarc initiating andstabilizing system, for. utilizing an oscillator having agridcircuittime constant greater than of a second so that the. initial impulsemaybe of greater, magnitudefthan subsequent impulses.

Other objects will inpartbe obvious, and will in part be explainedhereinafter; I

In practicing my invention in one of its forms, a blocking oscillator,which is normally biased to prevent oscillation, is keyed by a 60 cyclevoltage derived from an alternating current arc welding circuit. Theoutput of the blocking oscillator is fed through a cathode followerwhich is coupled to'the welding circuit for applying periodic voltageimpulses to the circuit for; initiatingand stabilizing a 60 cyclewelding arc therein.

For a more complete understanding -of the nature and scope of myinvention,"reference may be made to the following detailed descriptionwhich may be read in connection with the accompanying drawing, in which:I Fig. 1 is a diagrammatic view of an arc welding system embodying theinvention in one; of its forms, and

--Fig. 2 is a partial diagrammatic view of an arc welding system showingan alternate form of con-- nection of the arc initiating and stabilizingsystem to=thewelding circuit;

Referringto Fig. 1,v the reference numeralilfl may denote generally..anarc welding systemwherein a welding transformer l2 may be connected to asource ofcalternating current repre sented by .the conductors I3 forsupplying welding current to an arc welding circuit I5, including anelectrode. holder or weldingctorch. l'l andfwork i8 upon which a weldingoperation is'to be per formed. 5 .A' variable reactance device 20 may.be connected between thewelding, transformer, l2 and thewelding circuitI5"fo r controlling the. value of the welding current. V

An arc initiating and stabilizing system designated generally bythe-numeral 22 may be uti-.

lized for applying periodic voltage impulses to the welding torch I1for-initiating and stabilizing an are between the torch." and the workl8. The torch or holder I! may be of any suitable type, and for thepurposes of illustration, is shown as comprising, for example,atungsten' welding electrode having a hollow nozzle 25 positionedthereabouts, and'provided with suitable means,

such as the conduit connection, 21 for supplying an atmosphere of argonor helium gas to the welding zone. I

The are initiatin and stabilizing system 22v may comprise, generally, an.oscillator of the relaxation: type in which the frequencyis con-ctrolled byithe charge or discharge of a capacitor or inductance througha resistance, such :as, ior example, a blocking oscillator-circuit 30,which may be coupled to thearc welding circuit through a cathodefollower circuit 32 and conductor 33, which connects to the welding'leadsupplying welding current to thewelding electrode of the torchorholder IT. A' high frequency choke :34 may be interposed betweentheconnection of the conductor. 33 to the welding lead and the weldingtransformer l2, so as to block the voltage impulses of thearc initiatingand stabilizing system 22 from the welding transformer. V r I :Theblocking oscillator 30 may comprise, for example,ja four elementjvalvedevice 31 having afilament 38 connected to afilament transformer 39, acathode 40, a control grid 4!, a screen grid Hand an anode 43. Thescreen grid 42 may be connected tothe anode 43, and the anode-oath:

ode circuit of valve.3l maybe-connected toe suitablejsource ofdirect-current voltage s'uchas with the voltage of the arc weldingcircuit, a control transformer 55 may be utilizedto; apply 60 cycle biasboltage to the control grid 4| from the welding circuit for overcomingthe blocking bias of the cathode 40 and causingthe valve de- I Vice 31to oscillate and produceperiodic-voltage 1 impulses synchronized withthe voltage of; the arc welding circuit. A capacitor 5? may be conand aresistor 59 may be connected between the control transformer 55 and acontrol'jgrid 4 I, having such a Value that: the discharge time of thecapacitor 5'1 is on thezorder of /120 of a second.

A capacitor 80 may be connected between the,

high voltage side of the coupling 'transformer 52 and ground, and aresistor 62may be'icon'nected between the capacitor Bfl and therectifier device 45 so .as to increase the chargingtime of the capacitor65 so that the /so'of=a second between impulses of the blockingoscillator is insufficient to allow the capacitor 60 to charge to itsfull value. 1

The output of the blocking oscillator circuit 35 is fed into the cathodefollower circuit :32 which may, for example, comprise a four elementvalve device 65 having a cathode see control grid, 67!. and an anode 68.The valve device 65 may be supplied with a -direct current voltage ofrela-' tively high value from a. source of supply represented by therectifier device with its associated plate transformer 'l2.:andfilament-trans:- former 13. The output voltage of the rectifier.

device Ill may be-connected between the anode.

68 and the cathode 6E. The control grid Bl of the valve device 65 may beconnected to the blocking oscillator through a conductor '15., Thecathode follower circuit 32'may beconnected to the arc welding circuitthrough a capacitor "ll connected on the cathode side of a cathode'resistor'IS. I

In operation, the blocking oscillator 35 .will be. normally biasedagainst oscillating, by': reason of the positive bias applied to-thecathode 40 from the potentiometer 56.. Wheneverthe operator is ready toweld, a'60 cycle voltage may be applied to the control grid ll from thearc weding circuit 15 for driving the control grid positive whenever ingaction produced by the coupling transformer 52. Theapplication of thecontrol voltage from the arc welding circuit, I5 may be efie'cted by operating the control switch 56. which may either be located on the handleofthe-torch or holder H, or may comprise a portion of the foot switch(not shown) whih is usually usedto control the appli cation of gas tothe welding torch or holder.

Since the blocking oscillator has not'be'en previously operating, thecapacitor 60 Willbe initially charged to the full plate voltage of the'valve device 31, so that the first voltage'impulse produced therebywill be of amaximum value. Since the charging time for thecapacitor liilisgreater than /60 of a second, the capacitor lifl-wi'llnot be hillycharged on subsequent impulses, and hence the subsequent impulses willhave a lower peak value. The voltage impulses of the blocking oscillator30 are applied to the cathode follower circuit 32 through conductor 15,thus producing an amplified voltage impulse across the cathode resistor78. This voltage is applied to the welding electrode z ithroughcapacitorT1 and conductor 33 to provide a damped impulse for initiating andstabilizing an are between the welding electrode and the work I8.

7 Instead of using a shunt connection of the are initiating andstabilizing system 22 to the are welding circuit R5, the arc initiatingand stabilizing system may be series coupled with the arc weldingcircuit 'l5,- as shown in Fig. 2. The conductor 33 may for example, beconnected to the Y primary winding 80 of a coupling transformer 81,nected in the grid circuit of the valve device 31,

thes'ec'ondary winding 82 of which may be connected in series circuit.relation to the welding electrode 24 and the welding transformer l2., Inother-respects theeconnections of the arc initiating andstabilizingsystem, and the arc Welding circuit, may be identical with those shownin Fig. 1. =From the above description and the accompanying-drawing itwill be seen that I have provided in a simple, and: efiective manner forapplying periodic voltage impulses to. an arc welding:

circuit for initiating and stabilizing an are therein. By utilizingan-initial impulse of greater magnitude than". theisubsequent impulses,initiation of therarc is greatly facilitated'and' the duty cycle on theblocking. oscillator and cathode followerof the initiating andstabilizing system maylbe reduced during a Welding operation, when onlystabilization of :the arc is necessary. Sincejthe oscillator operatesonly'when th voltage'or the.

welding circuit is applied thereto for commenc ing a welding operation,the duty cycle thereof-i nection with an alternating current arc weldingsystem'in which the problem-of arc initiation and stabilization :becomesmore or less acute-particularly. at open circuit voltages on the orderof 65 volts, and when an inert gaseous atmosphere is used with atungsten electrode, the invention may beused advantageously ininitiating direct current arc welding operations with non-consum able orconsumable electrodes,- with 'or'without the inert gaseous atmosphere. I

(Since certain changes: may be made in the above-described construction;and different embodiments of the invention maybe made without departingfrom the spirit andsscope thereof, it is intended'thatall the mattercontained in the above description and shown in theaccompanying drawingshall be considered as illustrative.- and not in a limiting sense.

I claim-"as my invention:

' Theicombination with an'arc welding system including ania-rccircuit,of a relaxation oscillator, and a'puls'e generator. triggered by" theoscillator connected to apply. periodic voltage impulses to the arccircuit. 'z

2. --Inan alternating:- current arc welding systein'l anarc circuitincluding an electrode for maintaining an arc with work upon whichaweldeing operation is to be performed, a pulse generator disposed to producea direct current pulse, said pulse generator being coupled to theelectrode, an oscillator connected to trigger the pulse generator, andcircuit means connected to apply a control voltage to the oscillatorfrom the arc circuit.

3. An arc initiating and stabilizing system for an arc welding systemcomprising, a pulse generator disposed to produce a direct currentpulse, said pulse generator being coupled to the arc welding system, anoscillator connected'to trigger the pulse generator, and circuit meansconnected to apply a control voltage to the oscillator from the arcwelding system.

4. The combination with an arc welding system including an electrode forperforming a welding operation upon a workpiece, of a grid-controlledpulse generator connected to apply a relatively steep wave voltageimpulse between the electrode and the work, and a blocking oscillatorconnected to apply a periodic voltage pulse to the grid of the pulsegenerator.

5. In combination, an arc welding system including a welding transformerdisposed to supply alternating current to a welding circuit, a pulsegenerator operable to produce direct current impulses connected to thewelding circuit, a blocking oscillator connected to apply a periodiccontrol voltage to the pulse generator, and circuit means connected toapply a synchronizing voltage to the blocking oscillator.

6. The combination with an alternating current arc welding circuitincluding an electrode for performing a welding operation upon aworkpiece, of a grid-controlled pulse generator, circuit meansconnecting the pulse generator to the electrode for applying an arcinitiating and stabilizing impulse thereto, a blocking oscillatorconnected to apply a periodically recurring control voltage pulse to thegrid .of the pulse generator, and a control transformer connected in thewelding circuit arranged to apply a control voltage to the blockingoscillator.

7. An arc stabilizing system for applying a stabilizing impulse to anarc welding circuit comprising, a grid-controlled pulse generator,circuit means for connecting the pulse generator to the arc weldingcircuit, a blocking oscillator connected to apply periodic impulses tothe pulse generator, said blocking oscillator having aresistor-capacitor discharge circuit with a time constant greater thanthe period of said impulses.

8. In combination with an arc welding system including an electrode andwork connected in an arc circuit, a pulse generator connected to apply arelatively steep wave front impulse to the electrode, an oscillatornormally biased to prevent oscillation connected to key the pulsegenerator, and circuit means connected to apply a control voltage to theoscillator having a predetermined relation to the voltage of the arccircuit for initiating operation of the oscillator.

9. In an arc stabilizing system for an arc welding circuit, a pulsegenerator connected to apply voltage pulses to the arc welding circuit,a blocking oscillator normally biased against oscillation connected toapply control impulses to the pulse generator, capacitor means connectedin circuit relation with the blocking oscillator to provide a high peakvalue initial impulse, and circuit means connected to the weldingcircuit to supply a control voltage for overcoming the bias on theoscillator.

KENNETH N. FROMM.

No references cited.

